Turns out that there is in fact a list of sorts.
There were some days that the server was unavailable, and the domain was
added to this list.
The point of the list is unclear, but there is a list.
-----Original Message-----
From: Marcin Cieslak
Sent: Thursday, September 10, 2015 3:11 PM
To: Todd K Grand
Cc: nanog list
Subject: Re: outlook.com outgoing blacklists?
On Thu, 10 Sep 2015, Todd K Grand wrote:
The problem has been resolved.
Thanks to everybody that contributed.
And the issue was...?
~Marcin